Biol 202 Virology 2

E genes

early genes. involved in DNA replication and interfering with host immune responses.

L genes

late genes. involved in virion assembly and release.

dsDNA expression

coopts host mechanisms. DNA replicated, transcribed into mRNA, MRA translated into proteins

what viruses have dsDNA?

most phages, many important vertebrate viruses, herpesviruses, poxviruses

RNA virus gene expression

animal cells lack the mechanisms to replicate an RNA genome or transcribe mRNA from an RNA template. RNA viruses must supply their own enzymes somehow

+RNA gene expression

viral genome acts as mRNA. host cell synthesizes RNA-dependent RNA polymerase. builds -RNA, which acts as the template for +RNA

+RNA genome example

poliovirus

-RNA gene expression

cannot serve as mRNA. virus brings its own RNA-dependent RNA polymerase. +RNA intermediate is synthesized to act as mRNA and act as a template for -RNA

-RNA genome examples

filoviruses, rabies viruses, influenza virus

retrovirus gene expression

an RNA virus which brings its own RNA-dependent DNA polymerase (reverse transciptase). highly error-prone (no proofreading mechanism). uses integrase to insert viral DNA into host genome

dsRNA gene expression

host cell has no mechanism for dsRNA transcription or replication. virus brings its own RDRP transcriptase and replicase

dsRNA genome example

human rotavirus

virion assembly location

may be in cytoplasm or nucleus. may be seen as paracrystalline structures in cell.

bacteriophage virion assesmbly

occurs in stages

naked virion release

occurs as viral particles lyse host cell. viral proteins may attach peptidoglycan or membrane

enveloped virion release (budding)

viral proteins placed in the host membrane. nucleocapsid binds to them. host actin tails propel virion through host membrane

virion envelope source

Golgi or ER

bacteria and archaea are infected by

bacteriophages

virulent phage reproduction

multiplies immediately upon entry. lytic cycle.

temperate phage reproduction

may exhibitly lytic or lysogenic cycles.

lysogenic cycle

phage dwells in host cell without killing it. integrates own genome into host.

prophage

temperate phage genome that has integrated into host genome

archaeal phage reproduction

mosty temperate

temperate phage alterations to host phenotype

bacteria become immune to superinfection. phage may express pathogenic toxin or enzyme.

lysogeny advantages

phage remains viable, but does not kill host

induction

triggering of prophage into lytic cycle

virus enumeration techniques

direct virion count, or indirect count by observing a property

indirect virion count examples

haemagglutination assay, plaque-forming unit assay

PFU assay

diluted virus plated onto lawn of susceptible host cells. resulting cell death causes clear zones, called plaque.

bacterial/archaeal virus cultivation

requires susceptible host in log phage

animal virus cultivation cells

embryonic eggs or tissue cultures (ex vivo cells grown in vitro)

CPE

viral cytopathic effect (damage to host cells)

CPE manifestation

may be microscopic or macroscopic. may cause degenerative abnormalities. damage often related to host’s immune response (inflammation)

plant virus cultivation methods

cell cultures, protoplast cultures, whole plants

protoplast

a cell with wall removed

whole plant virus cultivation

localized necrotic lesions or generalized symptoms of infection